The present disclosure relates generally to interconnection packaging for integrated circuits and, more particularly, to a structure and method for wiring translation between grids having non-integral pitch ratios in chip carrier modules.
Integrated circuit chips may be packaged in a variety of ways, depending upon the performance and reliability requirements of the system in which they are used. High end integration schemes, sometimes referred to as multi-chip modules (MCMs) or single chip modules (SCMs), normally include at least one integrated circuit chip which is mounted to an insulating substrate. The insulating substrate, which may be ceramic, for example, has one or more wiring layers therein and thus provides a medium for electrical connections between chips (on an MCM) and/or between modules (for an MCM or a SCM). The wiring layers of the substrate are terminated at each of the top and bottom surfaces of the substrate in an array of I/O pads for interfacing to the chip and to a circuit board or other higher level module. The I/O pads may be a part of a controlled collapse chip contact (C4), ball grid array (BGA) or other connection scheme.
In a conventional MCM design, a logic service terminal (LST) grid (or via grid) located in the substrate provides an interface between the redistributed power, ground and signal terminals from a chip, and an X-Y wiring area. The X-Y wiring area comprises X and Y wiring planes which establish connections from one chip to another chip, or from one chip to pins on the MCM substrate. Typically, the LST grid has a pitch which is an integral multiple of the pitch of the chip I/O grid (e.g., C4 grid) for ease of interconnection therebetween. However, such a dependent relationship may be disadvantageous in that neither the LST grid nor the C4 grid may be changed or redesigned independently of one another.
In the event of a design change in the LST grid (e.g., for device miniaturization purposes), there is a resulting corresponding change to the C4 grid in order to maintain an integral multiple pitch ratio therebetween. As a result of a change in the C4 grid, there is also a change in chip design, wafer probes, temporary chip attachments (TCAs), and the like. Conversely, a design change in a C4 grid results a corresponding change in the LST grid. As a result, a design change in the LST grid begs certain technological advances in process fabrication areas such as ceramics, punch diameter, line width, masks, green sheet (GS) thickness, pastes, and the like. Thus, it can be seen that a design change in one grid aspect of an MCM may lead to costly changes in other aspects of the MCM.